This invention is directed to (i) treating compositions of a silicon atom containing hydrophobic-type treating agent and a silicon atom containing functional-type treating agent, (ii) filler particles treated with the composition, (iii) organic tire rubbers containing treated fillers, and (iv) methods of treating filler particles with a neat composition of the treating agents.
While United Kingdom Patent Application GB 2 355 453 A, published on Apr. 25, 2001, describes a neat treatment method for making hydrophobic calcium carbonate fillers for use in rubbers, the organosilicon treating agents used in the UK publication are not the same as the organosilicon treating agents used herein. The UK publication does show a polymethylhydrogensiloxane as a component of the treating composition for providing hydrophobicity to filler particles, but the UK publication fails to show a functional-type organosilicon compound containing sulfur as the other component of the treating composition.
Similarly, while U.S. Pat. No. 6,342,560 (Jan. 29, 2002) describes some organosilicon treating agents similar to the organosilicon treating agents used herein, the method of making hydrophobic calcium carbonate fillers in the ""560 patent is not via a neat treatment. Rather, the method of making hydrophobic calcium carbonate fillers in the ""560 patent is carried out in an aqueous suspension, and the ""560 patent fails to show a polymethylhydrogensiloxane as the component for providing hydrophobicity to the filler particles.
This invention relates to treating compositions suitable for applying to particles of a filler. The composition contains 5-95 percent by weight of a silicon atom containing hydrophobic-type treating agent, and 5-95 percent by weight of a silicon atom containing functional-type treating agent, based on the weight of the composition. In particular, the functional-type treating agent is a bis(alkoxysilylalkyl)polysulfide or a mercaptoorganosilicon compound, and the hydrophobic-type treating agent is a polyorganohydrogensiloxane or a silanol terminated silicone oligomer. The most preferred filler is precipitated (i.e., synthetic) calcium carbonate.
The invention also relates to fillers of particles treated with this treating composition, organic tire rubbers containing the treated fillers, and methods of treating particles of the filler with neat compositions of treating agents.
These and other features of the invention will become apparent from a consideration of the detailed description.
This invention is directed to the treatment of surfaces of precipitated calcium carbonate fillers with a treating composition containing treating agents which consist of hydrophobic-type silicon atom containing treating agents, and functional-type silicon atom containing treating agents. These treating agents are applied to the surfaces of the filler by a neat process.
Because of the treatment, it was unexpectedly discovered that the properties of rubber containing the treated fillers were much improved. In this regard, the hydrophobic-type silanes and siloxanes are used to impart to the particles of the reinforcing filler hydrophobicity for compatibility with organic rubbers, while the functional-type silanes and siloxanes provide bonding or coupling to the rubber network during its curing operation.
The term neat as used herein, is intended to mean that fillers are rendered hydrophobic and functionalized by applying the treating composition consisting of the organosilicon compounds or mixtures of the organosilicon compounds in their undiluted form. Thus, the organosilicon compound(s) is not dissolved, dispersed, combined, or mixed with another substance or ingredient, such as water, solvents, or carriers, as a solution, dispersion, or emulsion. To this extent, the treating composition is applied in a substantially pure condition.
The term functional, as it applies to organosilicon compound(s), is intended to mean that the compound contains groups capable of reacting with the surfaces of the filler and the rubber.
In one particular embodiment of the invention, therefore, hydrophobized and functionalized fillers were prepared by applying a treating composition containing a treating agent consisting of a methylhydrogenpolysiloxane as the hydrophobic-type treating agent. The functional-type treating agent present in the treating composition was the compound 3-mercaptopropyltriethoxysilane (MPTES), i.e., (C2H5O)3SiCH2CH2CH2SH, or the compound bis[3-(triethoxysilyl)-propyl]tetrasulfide (TESPT), i.e., (C2H5O)3SiCH2CH2CH2xe2x80x94Sxe2x80x94Sxe2x80x94Sxe2x80x94Sxe2x80x94CH2CH2CH2Si(OC2H5)3.
Characterization of properties of treated fillers was determined by Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer-Emmett-Teller Nitrogen Adsorption (BET). These analytical techniques showed the hydrophobic and SH functional treatments present on surfaces of precipitated calcium carbonate fillers. When evaluated in organic tire rubber formulations, rubber samples containing treated precipitated calcium carbonate fillers showed a higher modulus and an increased 300/100 modulus ratio, which reflect an improvement in tire mechanical performance.
The Filler Substrate (Precipitated Calcium Carbonate)
While any type of precipitated calcium carbonate can be used, it is preferably a precipitated calcium carbonate with a high surface area. Particularly preferred materials are rhombohedral calcites with specific surface areas of 20 m2/g. Such materials are generally available on a commercial basis from Solvay Interox, Houston, Tex., under Solvay""s trademark SOCAL 31(copyright).
The Functional-Type Treating Agent (Polysulfide)
This component of the treating composition comprises a bis(alkoxysilyl)polysulfide. Some general examples of bis(alkoxysilylalkyl)polysulfides which can be used include the bis(2-trialkoxysilylethyl)polysulfides in which the trialkoxy groups consist of trimethoxy, triethoxy, tri(methylethoxy), tripropoxy, tributoxy, or trioctyloxy, and in which the polysulfide is di-, tri-, tetra-, penta-, or an hexasulfide. Corresponding bis(3-trialkoxysilylpropyl)-, bis(3-trialkoxysilylisobutyl), -bis(4-trialkoxysilylbutyl)-, or bis(6-trialkoxysilylhexyl)polysulfide can also be used. Most preferred are the organosilanes including bis(3-trimethoxy-, -triethoxy-, and -tripropoxysilylpropyl)polysulfide; namely the di-, tri-, or tetrasulfide.
Specific examples of bis(alkoxysilylalkyl)polysulfides include compositions such as 3,3xe2x80x2-bis(trimethoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)tetrasulfide, 2,2xe2x80x2-bis(triethoxysilylethyl)tetrasulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(trimethoxysilylpropyl)hexasulfide, 3,3xe2x80x2-bis(trioctoxysilylpropyl)tetrasulfide, and their mixtures.
One most preferred compounds is 3,3xe2x80x2-bis(triethoxysilylpropyl) tetrasulfide (TESPT). TESPT is a commercial product marketed by Dow Corning Corporation, Midland, Mich. It is a mixture of 3,3xe2x80x2-bis(triethoxysilylpropyl)disulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)trisulfide, 3,3xe2x80x2-bis(triethoxysilylpropyl)tetrasulfide, and higher sulfide homologues having average sulfide contents of 3.5.
The Functional-Type Treating Agent (Mercaptoorganosilicon)
In another embodiment of the invention, the functional-type component of the treating composition may comprise a mercaptoorganosilicon compound instead of a bis(alkoxysilylalkyl)polysulfide.
Some representative examples of useful mercaptoorganosilicon compounds which can be employed herein are mercaptomethyltrimethoxysilane, mercaptoethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, mercaptomethyltriethoxysilane, mercaptoethyltripropoxysilane, 3-mercaptopropyltriethoxysilane, (mercaptomethyl)dimethylethoxysilane, (mercaptomethyl)methyldiethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and mixtures thereof. The most preferred of the compounds is 3-mercaptopropyltriethoxysilane (MPTES).
Some examples of useful blocked mercaptosilanes are 2-triethoxysilyl-1-ethyl thioacetate, 3-trimethoxy-silyl-1-propyl thiooctoate, bis-(3-triethoxysilyl-1-propyl)-methyldithiophosphonate, 3-triethoxysilyl-1-propyldimethylthiophosphinate, 3-triethoxysilyl-1-propylmethylthiosulfate, 3-triethoxysilyl-1-propyltoluenethiosulfonate, and their mixtures. By blocked is meant that the mercapto hydrogen atom is replaced by another group.
The Hydrophobic-Type Treating Agent (Polyorganohydrogensiloxane)
The hydrophobic-type component of the treating composition consists of a polyorganohydrogen siloxane of the formula: 
in which R1 and R2 represent alkyl groups containing 1-8 carbon atoms such as methyl, ethyl, isopropyl, and octyl; aryl groups such as phenyl, xenyl, naphthyl, and anthracyl; alkaryl (alkylaryl) groups such as tolyl and xylyl; aralkyl (arylalkyl) groups such as benzyl (phenylmethyl), phenylethyl (phenethyl), and 2-phenylpropyl; and cycloaliphatic groups containing 3-8 carbon atoms such as cyclobutyl and cyclopentyl. R1 can also be hydrogen. Typically, n has a value of 10-100, preferably 40-70. Such siloxanes generally have a viscosity of about 10 to about 1,000 mm2/s (centistoke).
The polyorganohydrogen siloxane used in the examples below was a trimethylsiloxy terminated polymethylhydrogensiloxane having a silicon bonded hydrogen content of 1.4-1.75 weight percent, and a viscosity of 20-40 mm2/s (centistoke). The composition is commercially available from the Dow Corning Corporation, Midland, Mich.
The Hydrophobic-Type Treating Agent (Silanol Terminated Silicone Oligomer)
In an alternate embodiment of the invention, the hydrophobic-type component of the treating composition may comprise a silanol terminated silicone oligomer, instead of the polyorganohydrogen siloxane above. The silanol terminated silicone oligomer has the formula: 
in which R3 is an alkyl group containing 1-8 carbon atoms such as methyl, ethyl, isopropyl, and octyl; an aryl group such as phenyl, xenyl, naphthyl, and anthracyl; an alkaryl (alkylaryl) group such as tolyl and xylyl; an aralkyl (arylalkyl) group such as benzyl (phenylmethyl), phenylethyl (phenethyl), and 2-phenylpropyl; or a cycloaliphatic group containing 3-8 carbon atoms such as cyclobutyl and cyclopentyl. Typically, m has a value in the range of 1-10. Such oligomeric siloxanes generally have a viscosity of about 20 to about 800 mm2/s (centistoke).
The silanol terminated silicone oligomer used in the examples was a hydroxyl endblocked polydimethylsiloxane fluid having a viscosity between 38-45 mm2/s (centistoke), in which m is about 6, and wherein the xe2x80x94OH content is between 3.9-4.3 weight percent.
This particular embodiment of the invention is unique to the extent that the silanol terminated silicone oligomer contains dimethyl units in the molecule which are capable of providing the hydrophobing characteristic needed, as well as xe2x80x94OH containing units capable of providing the functional characteristic needed, i.e., reactions (coupling) between the surface of the filler particles and the rubber surfaces in which the filler is employed, and/or with other coupling agents present in the treating composition.
Filler particles can be treated with the treating composition (i) by applying the hydrophobic-type treating agent and the functional-type treating agent to filler particles at the same time, (ii) by applying the hydrophobic-type treating agent and the functional-type treating agent to filler particles sequentially, (iii) or by first premixing the hydrophobic-type treating agent and the functional-type treating agent, and then applying the mixture to filler particles.
Application of the treating composition to the filler particles can be carried out at temperatures ranging from xe2x88x9220xc2x0 C. to 200xc2x0 C., preferably room temperature (20xc2x0 C.-25xc2x0 C.). The treated filler particles are then heated to temperatures of 100xc2x0 C.-150xc2x0 C. for one minute to 24 hours, to cause surfaces of the filler particles to react with the treating composition.
The treating composition is applied to the filler particles in the amount of 1-15 percent by weight, based on the weight of filler particles being treated. The treating composition contains 5-95 percent by weight of the hydrophobic-type treating agent, and 5-95 percent by weight of the functional-type treating agent, based on the total weight of the treating composition.